In an optical transmitter, in order to prevent decrease in the current-light conversion efficiency (slope efficiency) of a semiconductor laser used for the optical transmitter due to a temperature rise, and prevent a wavelength shift due to the temperature, a thermoelement that is represented by a Peltier device or the like and that heats or cools the semiconductor laser by using a current, and a TEC (Thermo-Electric Cooler) controller that controls the thermoelement are typically disposed to keep the semiconductor laser at a constant temperature in conventional temperature control using the TEC controller, the temperature at which to drive the semiconductor laser is determined, the current temperature information about the semiconductor laser is read by a temperature sensor such as a thermistor, information including a current, a voltage and so on, which correspond to the temperature, is fed back to the TEC controller, and the TEC controller controls the temperature of the thermoelement (i.e., the temperature of the semiconductor laser) in such a way that the current, the voltage and so on are kept constant.
Further, for example, patent literature 1 discloses a thermal control circuit in which a laser diode is disposed as a pumping light source, and a heating/cooling discrimination circuit acquires a high-low relationship between a temperature detected by a temperature detector and a target temperature set arbitrarily, and a control block controls the time ratio of ON/OFF of a current for driving a control element on the basis of this high-low relationship in such a way that the temperature of the control element becomes equal to the target temperature.